2009 SURE Projects

Advisor

Department

Prof. Marc Achermann

Department of Physics

A. Optical Characterization of Nanomaterials

Our research focuses on the optical spectroscopy of nanoscale materials, specifically semiconductor, metal and organic nanostructures. We study the carrier and energy relaxation dynamics of nanostructures and the dynamics of interfacial interactions in hybrid excitonic/plasmonic materials. Understanding this behavior in functional nanomaterials will promote the implementation of these materials in solid-state lighting, sensor, and light-harvesting applications (e.g. solar cells). In addition to standard, steady-state optical characterization, our experiments rely on various time-resolved optical spectroscopy techniques in combination with far- and near-field optical microscopies.

Prof. Mike Barnes

Department of Chemistry

B. Single molecule spectroscopy of optoelectronic nanomaterials

This project will involve assisting in experiments probing hotophysical properties of individual hybrid nanostructures comprised of an inorganic semiconducting core and conjugated organic ligands coordinated to the core surface. The REU student will be involved in both experimental preparation, fluorescence lifetime imaging and data analysis.

Developments of asymmetric colloidal particles have largely demonstrated proof-of-principle concepts with a relative lack of functionality. We propose to modify surface (spatially and chemically distinct) proteins by incorporating hydrophobic elastin-like polypeptide motifs. Characterization of resulting particles will be assessed by various microbiological assays, light scattering techniques, and circular dichroism.

Prof. Surita Bhatia

Department of Chemical Engineering

D. Biomimetic Nanocomposites

Prof. Al Crosby

Department of Polymer Science & Engineering

E. Nanoparticle Assemblies for Tailored Mechanical Properties

From the wrinkles on our skin to the snapping of the Venus Flytrap, instabilities are ubiquitous in Nature fore defining shape, structure, and function. We use elastic and fluid instabilities to create novel hierarchical structures in polymer nanocomposites. Taking advantage of true nanoscale effects of nanoparticles in polymer matrices, we design assemblies that will alter their nanostructure upon application of mechanical energy to extend the material's ductility.

Polarizable nanoparticles and colloidal particles bound to a surface present a unique opportunity to generate complex, equilibrium order, tunable through the use of external fields (electro-magnetic). As such, this system holds strong promise for a broad range of nano- technology applications, in which precise and predictable control long- range patterning is required. When the dipolar orientation of these particles are uniformly perpendicular to the absorbing surface, neighboring particles experience a long-range, dipolar repulsion. In the presence of a competing short-ranged interaction, such as depletion-induced attraction, the system becomes frustrated, resulting in a variety of "mesophase-ordered" particle assemblies. In mesophases, many particles "clump" into composite clusters which are themselves arranged in a variety of geometric motifs: discs, stripes and networks. This project will model the thermodynamics of mesophase assembly in polarized nanoparticle systems. Specifically, we seek to predict how the size and shape of nanoparticle clusters may be tuned by through the control of external fields and/or inter-particle forces.

Prof. Murugappan Muthukumar

Department of Polymer Science & Engineering

G. Molecular Modeling of Polymer Translocation

This project focuses on movement of polynucleotides and proteins through protein channels.

Prof. Mike Maroney

Department of Chemistry

H. Biohybrid Materials for Hydrogen Generation and Utilization

The proposed project involves the design and synthesis of materials for the production and utilization of hydrogen, using an approach involving the replacement of the electron donor or the drain (acceptor) in the physiological systems with judiciously chosen semiconductors. The work involves isolation and purification of hydrogenase, and modification of surface residues for covalent attachment to semiconductor materials. If successful, the catalytic properties of the materials will be characterized.

Herein, we introduce synthetic guanidinium-rich polymers which compared to polyarginine are more hydrophobic and have a more shape-persistent scaffold, namely polyguanidino-oxanorbornene (PGON) transporters. We provide an extensive characterization of their membrane activity including the dependence on pH, concentration, length, membrane fluidity, membrane and surface potential. The global responsiveness of these transporters reveals significant differences when compared with similar systems. Their overall ability to respond to chemical stimulation by both activation and inactivation is similar to CPPs, although PGONs show different selectivities than CPPs. These findings imply that PGON-counterion complexes could act as multicomponent sensors in complex matrices, a promising application of membrane transporters that attracts current scientific attention but has so far been limited to synthetic multifunctional pores. Lactate sensing in milk, with lactate oxidase for signal generation and Cascade Blue (CB) hydrazide for signal amplification, is used to demonstrate their potential in this area. We thus believe that PGONs could serve as an easily accessible membrane transporter, which complements the toolbox of available optical signal transducers in analyte sensing across membranes.

M. Novel hydrogels with tunable properties

Hydrogels have gained interest in the area of biomaterials for their many attractive qualities including high water content, porous structure, and tunable gelation conditions. These qualities allow the integration of such materials in the body as tissue scaffolds by offering structural support and allowing influx of cell metabolites and efflux of cell waste through their pores. Of even greater interest is to design hydrogels that can incorporate cells in a three dimensional structure while eventually degrading to leave behind only healthy tissue. In general ABA amphiphilic block copolymers form associative networks in water where the A block is hydrophobic and the B block is hydrophilic. This self-assembly is driven by the association of the hydrophobic endblocks into micellar structures, which are bridged by the water-soluble midblocks and form physically crosslinked networks. These physical hydrogels are attractive because no crosslinking agent is necessary and the gelation can be triggered by physically relevant stimuli (body temperature and pH). However, a number of groups have chemically crosslinked these polymers as well. Chemical crosslinking leads to a more permanent three-dimensional structure than the physically crosslinked counter-parts, but can still be degraded with time, and can be modified to incorporate proteins or adhesion peptides to increase the adhesion of cells to the scaffold.

Prof. Sankaran Thayumanavan

Department of Chemistry

N. Polymeric Nanostructures Towards Enhancing Solar Cell Performance

The fundamental challenge in materials for photovoltaics is to enhance the efficiency of charge-separated states and/or slow down charge recombination. Incorporating the elements of photovoltaics within organized nanoscale assemblies is a promising approach towards achieving this goal. In this direction, Thayumanavan group is involved in achieving morphologies that one could obtain using block copolymers or nanoporous templates containing photoactive and charge transport units in the appropriate domains. These efforts will provide fundamental insights into the structure-property relationships in terms of the roles of individual molecules vs. bulk morphology in the overall performance of the materials as components of solar cells.

Prof. Dhandapani Venkataraman

Department of Chemistry

O. Photovoltaic Devices Based on Inorganic Semiconductors

In hybrid photovoltaic cells, semiconductor nanoscale structures are used as electron conductors. For efficient charge transport, the length of the nanoscale structures should be on the order of micrometers and the width of the rod should be in nanometers. Moreover, the semiconductor rods should be oriented perpendicular to the electrode surface for efficient charge collection. Our approach involves the use of electrochemical deposition within the pores of a nanoporous template and the removal of template after the deposition. Our work involves optimization of electrochemical conditions to obtain the targeted phase of the semiconductors in a crystalline form and fabricate photovoltaic devices.

P. Photovoltaic Devices Based on Organic Semiconductors

For efficient organic or hybrid photovoltaic cells, hole-conducting and electron-conducting organic moieties need to be assembled into segregated structures. This allows the exciton to split at the interface. Yet, it is favorable for hole-conducting moieties mix with electron-conducting moieties. How do we keep them separated? Our approach involves appending groups to electron-rich and electron-poor moieties such that the interaction between these groups will be unfavorable. The underlying hypothesis of our approach is that mixing of electron-rich and electron-poor moieties will be disfavored because of the immisciblity between the groups appended on them.